1. Field of the Invention
The invention relates to communication systems, and in particular to communication systems wherein a user may register an identity from multiple locations.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication between two or more entities such as user equipment, communication network elements and other entities associated with the communication system. A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment or terminal is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable communication by means of the system.
Communication systems proving wireless communication for user equipment are known. An example of the wireless systems is the public land mobile network (PLMN). The PLMNs are typically based on cellular technology. In cellular systems, a base transceiver station (BTS) or similar access entity serves mobile stations (MS) or other such wireless user equipment (UE) via a wireless interface between these entities. The communication between the user equipment and the elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected. One or more gateway nodes may also be provided for connecting the cellular network to other networks. e.g. to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched networks.
An example of the services that may be offered for user such as the subscribers to a communication systems is the so called multimedia services. Some of the communication systems enabled to offer multimedia services are known as Internet Protocol (IP) Multimedia networks. IP Multimedia (IM) functionalities can be provided by means of a IP Multimedia Core Network (CN) subsystem, or briefly IP Multimedia subsystem (IMS). The IMS includes various entities for the provision of the multimedia services.
The communication systems have developed in the direction wherein various service provision functions of the network are handled by network entities known as servers. For example, in the current third generation (3G) wireless multimedia network architectures it is assumed that several different servers are used for handling different functions. These include functions such as the call session control functions (CSCFs). The call session functions may be divided into various categories such as a proxy call session control function (P-CSCF), interrogating call session control function (I-CSCF), and serving call session control function (S-CSCF). It shall be appreciated that the CSCFs may be also referenced to as the call state control functions.
Communication systems may be arranged such that a user, typically a subscriber, has to initiate communications over the communication system. For example, a user may request for a session, transaction or other type of communications from an appropriate communications network entity. Such communications can be seen as being originated from the user. From the above discussed network entities the serving call session control function (S-CSCF) forms the entity the user needs to be registered at in order to be able to request for a service from the communication system.
In certain specifications, such as the 3GPP Release 6, which is currently the latest version of the 3GPP specifications, the IMS networks are configured so as to allow the user to register a single public user identity from multiple locations using more than one contact addresses The multiple contact addresses may even relate to different terminals having access to multiple access networks. For example, the user may access the IMS via GPRS and/or WLAN networks with appropriate user equipment.
When proxying incoming requests, the network has the choice to route the request to all the registered contact addresses or only some of them. In order to make the most appropriate routing decision, the network needs some sort of preference settings both from the user and the network on handling the multiple contacts. More specifically, the network needs to decide whether it should fork a request or not. Subsequently, if forking is to be used, a decision is needed if sequential search or parallel forking is preferred. If sequential search is preferred, then it needs to be decided in what order the different contact addresses associated with the registered user identity should be contacted.
Internet Engineering Task Force (IETF) document RFC 3261 “SIP: Session Initiation Protocol” by J. Rosenberg, et al., June 2002, describes the concept of sequential search. The RFC 3261 document is incorporated herein by reference. In the sequential search a sequential trial is performed with multiple contacts based on the user's preference given by the so called q (preference) value. The q value is a parameter attached to the contact address, such as a Uniform Resource Identifier (URI). If an attempt to contact the most preferred contact fails, then the next preferred is tried, until a final response is received from one of the contact addresses. The RFC 3261 also describes the concept of parallel forking. In the parallel forking the different addresses are contacted simultaneously at the same time. That is, the network forks the incoming request to all of the registered contacts at the same time. Using the q values according to RFC 3261, the called party is able to manipulate per registration basis the preferences on handling the registered multiple contacts.
A proposal is that the caller can also indicate her preferences on handling a certain request. The caller preferences may overrule the called party preferences. This may be performed by using of a specific header field, i.e. the ‘Request-Disposition’ header field. The field specifies caller preferences for how a server of the terminating network should process the request where this header field is included. This has been proposed to be performed by using the following directives. A fork-directive is proposed to indicate whether a proxy should fork a request (“fork”), or proxy to only a single address (“no-fork”). If the server is requested not to fork, the server should proxy the request to the “best” address. The best address would normally be the one with the highest q-value. In case the fork-directive is set to “fork”, then a parallel-directive indicates whether the caller would like the proxy server to proxy the request to all known addresses at once (“parallel”), or go through them sequentially, contacting the next address only after it has not received a final response for the previous one (“sequential”).
However, if neither the called party preferences nor caller preferences are defined, the network behavior might be ambiguous. The terminating proxy server may require some configuration how it should behave in this “default case”.